Stock flow control system for a headbox

ABSTRACT

A CONTROL SYSTEM FOR A HEADBOX CONTROLLING THE VARIABLES EFFECTING THE FORMATION, WEIGHT AND OTHER CHARACTERISTICS OF A PAPER WEB FORMED. IN THE PREFERRED EMBODIMENT THERE IS A CONTINUOUSLY MOVING FORMING WIRE WHICH RECEIVES STOCK PASSING THROUGH A SLICE IN THE HEADBOX. THE SYSTEM INCLUDES A SENSING DEVICE FOR GENERATING A FIRST CONTROL SIGNAL INDICATIVE OF THE SPEED OF THE FORMING WIRE, A TRANSDUCER DEVICE FOR GENERATING A SECOND CONTROL SIGNAL INDICATIVE OF THE OPEN AREA OF THE SLICE, AND A SENSING DEVICE FOR GENERATING A THIRD CONTROL SIGNAL INDICATIVE OF THE STOCK FROM A STOCK SUPPLY CHEST. THE THREE CONTROL SIGNALS ARE SUPPLIED TO A STOCK FLOW CONTROL UNIT AND A TOTAL FLOW CONTROL UNIT, WHICH CONTROL THE FLOW OF   STOCK FROM THE SLICE SUCH THAT THE RATIO STOCK VELOCITY TO FORMING WIRE SPEED MAY BE MAINTAINED CONSTANT OR VARIED AT WILL.

Feb. 9, 1971 J. w. TAYLOR STOCK FLOW CONTROL SYSTEM FOR A HEADBOX 3 Sheets-Sheet l Filed April 14, 1967 I l By uw @M @141-5 M10/Mms Feb. 9, 1971 J. w. TAYLOR STOCK FLOW CONTR() SYSTEM FOR A HEADBOX 3 SheetseSheet Filed April 14, 1967 BY /Qkw A46.. A? rola/vub- Feb. 9, 1971 J. w. TAYLOR 3,562,104

STOCK FLOW CONTROL SYSTEM FOR A HEADBOX United States Patent O U.S. 'CL 162-253 8 Claims ABSTRACT F THE DISCLOSURE A control system for a headbox controlling the variables effecting the formation, weight and other characteristics of a paper web formed. In the preferred embodiment there is a continuously moving forming wire which receives stock passing through a slice in the headbox. The system includes a sensing device for generating a iirst control signal indicative of the speed of the forming wire, a transducer device for generating a second control signal indicative of the open area of the slice, and a sensing device for generating a third control signal indicative of the stock ow from a stock supply chest. The three control signals are supplied to a stock flow control unit and a total flow control unit, which control the flow of stock from the slice such that the ratio of stock velocity to forming wire speed may be maintained constant or varied at will.

BACKGROUND OF THE INVENTION -Field of the invention This invention relates generally to a method and apparatus for controlling the flow of stock to a headbox, and more particularly to a method and apparatus for controlling the flow of stock to a headbox and the velocity of the stock leaving the slice of the headbox and merging with a forming wire. Specifically, the present invention is directed to a method and apparatus for sensing various functions of a paper making machine as the stock is delivered to the forming wire and generating control signals indicative of such functions to control the ow of stock onto the :forming wire.

Description of the prior art One approach to automating or controlling the paper making process is the stepwise, systematic organization of functional sections into stabilized control units. Often the stabilization of one function, or section, of a machine or a process reduces or eliminates variations in succeeding parts or steps of the continuous process. Ultimate supervisory control of the complete operation is required to observe each step of the process.

SUMMARY OF THE INVENTION Briefly, the present invention provides means for controlling the operation of the forming wire and the headbox in such a manner as to provide uniform stock ow onto the forming wire per unit length of travel thereof. A speed sensing device is coupled to the couch roll adjacent the slice to generate a control signal indicative of forming wire speed. Also, means are provided for sensing the open area of the slice and generating a control signal indicative thereof. These control signals are combined in a flow control circuit, which, in turn, controls the vow of stock to the headbox in acocrdance with the sensed conditions.

Accordingly, one of the primary objects of the present invention is to provide a stock flow control system which is inexpensive, simple to operate and which requires a minimum number of control signals for the proper operation thereof.

Patented Feb. 9, 1971 Another object of the present invention is to provide a flow control system which includes means for: orderly and safe start-up of a headbox or forming unit; accurate control of the ratio of the spouting velocity to forming medium speed; continuous and stable control of velocityspeed ratio during acceleration and deceleration of the forming wire speed at any given speed; and adjustable dilution water rate at constant ratio of stock velocity and forming wire speed; and constant basis weight control over a given speed range.

These and other objects, features and advantages'will be more fully realized and understood from the following detailed description when taken in conjunction with the acompanying drawings in which like reference numerals throughout the various views of the drawings are intended to designate similar elements or components and wherein:

BRIEF DESCRIPTION OF' THE DRAWINGS` FIG. 1 is a schematic diagram illustrating a control system for a headbox which is constructed in accordance with the principles of this invention;

FIG. 2 is a schematic block diagram showing the connection of the stock flow control and the total flow control shown in FIG. 1;

FIG. 3 is a chart illustrating the range of adjustment of stock flow to maintain constant basis weight over a wide range of speed of the forming wire;

FIG. 4 is a chart illustrating the range of adjustment of ratio of stock velocity and forming wire speed; and

FIG. 5 is a chart illustrating the typical characteristic curve of a ilow control valve of FIG. l, before and after correction by the valve positioning relay.

DESCRIPTION OF THE PREFERRED EMBODIMENT By way of background, the discharge velocity of the stock .through the slice is equal to the total amount of stock delivered to the slice -divided by the total area of the slice opening, and is represented by the formula v=kQ/A, where Q represents the total delivery in gallons per minute (g.p.m.), A is the slice opening, and k is a constant of proportionality which may include slice width, volume, etc.

On one type of headbox, the slice opening is considered to be the roof or throat opening above the apron lip at the point of discharge over the suction breast roll beneath the forming roof. On another type of headbox, the height of the slice knife edge above the rigid apron lip is the area considered. This dimension can be the average of the front-side and back-side portions of the slice, or the average of the knife edge slice screw positions added algebraically to the gate height.

At a given forming wire speed, the ow of thick stock to the headboX is a function of the sheet basis weight, as shown in FIG. 3. Changes in weight require proportionate changes in heavy stock ow at constant forming wire speed. Also, at a given weight setting, the speed of the forming wire can be varied while maintaining a constant basis Weight.

Changes in the flow rate of the dilution water at constant forming wire speed and tonnage result in a proportionate change in the headbox consistency while maintaining a constant ratio of stock velocity to forming wire speed, as shown in FIG. 4. It will be understood throughout the specification and claims that the expression V/S is intended to designate the ratio of the spouting velocity to the forming wire speed.

Therefore, at a given forming wire speed, the water ow to the headbox is a function of the open area of the slice and the selected velocity to speed ratio. Changes in forming wire speed will cause the velocity of the stock flowing from the slice to change to a new velocity such that the result is a constant V/S ratio. The water 3 tlow rate of the dilution water can be changed by adjusting the slice opening. Therefore, the water ow rate will change in response to the open area of the slice such that the velocity of the stock passing through the slice will maintain a constant V/ S ratio. That is, the larger slice opening requires a higher flow rate to maintain a given discharge velocity. On other hand, a. smaller slice opening requires a lower flow rate. Manual adjustment of the ratio of stock spouting velocity to forming wire speed will likewise require a new flow rate based upon the formula v=kQ/A. Similarly, a change in machine speed will require a corresponding change in the flow rate of stock to the headbox to maintain the desired V/S ratio.

For a better understanding of the present invention, reference is now made to FIG. l wherein a headbox is provided for supplying a slurry of stock to a forming wire 11. The forming wire 1.1 wraps a couch roll 12 which, in turn, is connected to a speed sensing device 13. The speed sensing device 13 senses the revolutions per minute of the couch roll 12, and generates a control signal indicative of forming wire speed.

The open area of the slice of the headbox 10 is controlled by a pair of slice lift units 14 and 15 which, in turn, are connected to sensing devices 16 and 17 respectively. 'I'he sensing units 16 and 17 may be positioned at opposite ends of the slice across the machine to insure that the opening of the slice is uniform in the cross machine direction. The control signal generated by the sensing devices 16 and 17 together with the control signal generated by the speed Sensing device 13 are combined to control the ratio of the stock velocity leaving the headbox to the forming wire speed. Also, these control signals are used to maintain a constant basis weight of the stock.

The control signal from the speed sensing device 13 is delivered via the broken line 18 to a stock flow control unit 19. The output of the stock ow control unit 19 is connected to a heavy stock ow control valve 20, while Aa stock ow meter 21 has a signal output thereof contive to the forming wire Speed and the stock spouting velocity so as to maintain a constant basis weight per unit length of forming wire travel.

The stock owing through the heavy stock control valve passes through a stock delivery pipe 22a to a junction 22b whereupon a supply of dilution water 26 is added to the stock prior to the stock being delivered to the headbox 10.

The diluted stock enters a fan pump 27 which delivers the stock to the headbox with suitable pressure and volume. The output of the fan pump 27 is connected to a stock delivery pipe 28 which, in turn, is connected to a total headbox ilow valve 29. The flow valve 29 controls the total ow to the headbox which includes the stock from the stuff box 23 and the dilution water from the supply 26.

The stock leaving the ow control valve 29 enters a tapered stock distributor 30 via a stock delivery pipe 28a. The tapered stock distributor 30 is connected to a plurality of stock inlet tubes 31 which deliver the stock to the interior of the headbox 10i. The function of the tapered manifold 30 is to provide uniform pressure distribution across the manifold so that the stock is delivered to each of the inlet tubes 31 with the same pressure.

The reduced diameter portion of the stock distributor 30 is connected to a pump 32 and to a manually adjustable valve 33 which controls the recirculation of the stock from the output of the distributor 30 to the input thereof. The manually adjustable valve 33 also serves to control the pressure gradient within the distributor 30.

A total flow control unit 34 is connected to and in control of the control valve 29. The control signal generated by the speed sensing device 13 is delivered to the total ow control unit 34, and the control signal from the sensing devices 16 and 17 is delivered to the total flow control unit 34 such that the two control signals are combined to control the opening of the ow control valve 29. Also, connected in fluid communication with the ow control valve 29 is a flow sensing unit 36 which generates an output signal indicative of the flow of stock therethrough. The output signal from the flow sensing unit 36 is delivered to the total ilow control unit 34 and the three control signals are combined to control the operation of the stock delivery system.

For a better understanding of the stock flow control unit 19 and of the total control unit 34, reference is made to FIG. 2. The stock flow meter 21 is connected to a flow controller 40. Also connected to the flow controller 40 is the breast roll speed tachorneter 13 through a ratio adjusting controller 41. A basis weight control 42 and a basis weight adjusting station 43 are connected to the ratio adjusting controller 41 so that a desired predetermined basis weight per unit length of forming Wire may be selected. The combined signals to the flow controller 40 are delivered to a manual-auto selector station 44 which, in turn, is connected to a valve positioning relay 46. The output of the valve positioning relay 46 is connected to the stock flow control valve 20 to control the operation thereof.

The breast roll speed tachometer 13 is also connected to a ratio adjusting controller 47 which is provided with a V/S adjustor 48. The output of the ratio adjusting controller 47 is delivered to a ratio adjusting controller 48 which, in turn, also receives the output signal from the slice position transducers 16, 17. The output of the ratio adjusting controller 48 together with the control signal from the water flow meter 36 are delivered to a flow controller 49 which, in turn, is connected to a manualauto selector station 50. The output of the selector station 50 is delivered to a valve positioning relay 51 to control the water llow valve 29.

As seen in FIG. 3, the chart illustrates the flow of thick stock to the headbox as a function of forming wire speed to maintain a given basis weight. Changes in basis weight require proportionate changes in heavy stock ow for a given constant speed operation. At a given basis weight setting, the speed of the paper forming operation may be varied.

The chart in FIG. 4, indicates the web speed as a function of the headbox total flow rate to obtain a constant V/S ratio. Any changes in water rate at constant speed and tonnage result in a proportionate change in headbox consistency while maintaining a constant ratio of spouting velocity to forming Wire speed.

The chart in FIG. 5 indicates the conguration of the control valves used to control the ow of stock in the present invention. The control valves are equipped with cam-operated positioning relays which permit linearization of the llow rate with that of the control signal. Thus, a feed-forward impulse sets the control valve at nearly the required position for proper system operation. A calibrated positioner cam, as indicated by the chart in FIG. 5, can compensate for valve port characteristics, pump characteristics and piping friction over the control ow range.

In operation, the control signal from the speed sensing device 13 is used as the master control index which indicates a feed-forward or anticipatory control function. Therefore, increasing the speed of the forming wire will cause both the stock flow control valve 20` and the total flow control valve 29 to open a proportionate amount. The amount of control valve movement is determined by the calibration of the ratio adjusting controller 41, the flow controllers 40 and 49 and the valve positioning relays 46 and 51.

As mentioned hereinabove, the control valves are equipped with cam-operated positioning relays which permit linearization of flow rate with the control signal. Thus, the feed forward inpulse sets the control valve at the required position for proper system operation. Reset or integrating action of the flow controllers 40` and 49 continues to open the corresponding control valves until the required flow is sensed by the fiow indicators 21 and 36 and a signal is fed back to balance the master input signal. At this point, control action of the fiow valves cease until a system change is encountered whereupon corrective action is automatically accomplished by the stock flow control unit 19 and the total flow control unit 34.

The basis weight adjustment is provided to change the ratio of stock flow to forming wire speed. This adjustment changes the slope of the family of curves as indicated in FIG. 3.

For opration of a hydraulic slice on the headbox 10, the wet end of the paper making machine should start up at slow speed with fan pump 27 starting at approximately 400 ft. per minute to prevent a high velocity surge of stock to the forming wire. When the control system is in automatic operation, the water and stock valves will track the increasing machine speed While maintaining sufficient sheet basis weight on the forming wire. This satisfies the first requirement for a safe and orderly start-up of the wet end of a paper making machine. The other requirements are met by the following operating abilities under full automatic control. For example, at constant speed, the basis weight can be increased or decreased by adjusting the manual input control 42, which may be provided on a panel. Also, headbox consistency can be increased or decreased simply by increasing or decreasing the slice or throat opening without effecting the V/S ratio or basis weight. In addition, the stock spouting velocity to forming wire speed ratio can be changed by adjusting the manual input of the selector stations 44 and 50. By utilizing the stock ow control system of the present invention, the speed of the forming Wire can be changed while maintaining a constant basis weight, maintaining a constant V/S ratio, and maintaining a constant headbox consistency. The paper making machine could, therefore, be operated at maximum drying capability by varying the machine speed slightly to obtain the desired moisture level at the take off reel.

Automatic grade changes can be programmed into the control system from a higher intelligence level such as a human operator or process supervisory control system. Speed, basis weight, V/S ratio and total water rate controls are readily accessible to -manipulation either manually or remotely.

A basis weight measurement device 60 may be incorporated into the system and connected to the stock flow control unit 19 to deliver thereto control signals indicative of the actual basis weight measured at the dry end of a paper making machine. In operation, the basis weight adjustor 42, of FIG. 2, is set to the desired basis weight, and thereafter, as sensed at the dry end of the paper making machine the measurement device 60` will generate a control signal indicative of actual basis weight and compare this signal with the selected basis weight of device 42. Therefore, if the actual basis weight is different than the selected basis weight a correcting signal is developed and delivered to the stock flow control unit 19 which, in turn, controls the heavy stock control valve 20.

Therefore, the present invention has provided means for controlling the stock delivery to a headbox such that a constant basis weight, constant V/S ratio, and the total water rate can be controlled with a minimum control signal.

It will be understood that variations, and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

I claim as my invention:

1. In a paper making machine including:

a continuously moving porous forming surface;

a headbox for receiving a slurry of paper stock, said headbox positioned in close proximity with said surface;

a slice formed in said headbox adjacent said surface for delivering stock to said surface;

means for supplying stock;

stock delivery means connected between said headbox and said supply means for delivering stock to said headbox;

the improvement therein comprising speed sensing means for sensing the rate of travel of said surface and generating a first control signal in response thereto;

first stock flow control means connected in fluid cornmunication with said stock delivery means for controlling the amount of stock delivered to said headbox;

first signal conversion means connected to said first stock flow control means and connected to said speed sensing means for receiving said first control signal whereby variations in the rate of travel of said surface will cause a corresponding change in said first stock flow control means to change the amount of stock delivered to said headbox;

adjusting means for changing the open area of said slice;

transducer means for sensing the amount of open area of said slice and generating a second control signal indicative thereof, whereby the velocity of the stock passing through said open area onto said surface is a function of said open area and quantity of stock delivered to said headbox,

second stock tiow control means connected between said first stock control means and said headbox, and

second signal conversion means connected to said second stock control means and receiving said first and second control signals to control stock flow.

2. In a paper making machine including:

a continuously moving porous forming surface;

a headbox for receiving a slurry of paper stock, said headbox positioned in close proximity with said surface;

a slice formed in said headbox adjacent said surface for delivering stock to said surface;

means for supplying stock;

stock delivery means connected bet-Ween said headbox and said supply means for delivering stock to said headbox;

the improvement therein comprising speed sensing means for sensing the rate of travel of said surface and generating a first control signal in response thereto;

4first stock flow control means connected in fluid communication with said stock delivery means for conrolling the amount of stock delivered to said headfirst signal conversion means in control of said rst stock flow control means and connected to said speed sensing means for receiving said first control signal whereby variations in the rate of travel of said surface will cause a corresponding change in said first stock flow control means to change the amount of stock delivered to said headbox;

slice sensing means generating a second control signal in response to the open area of said slice;

second stock flow control means connected between said rst stock control means and said headbox; and second signal conversion means connected to said second stock control means and receiving said first and second control signals, and connected to control the tiow of stock to said headbox.

8 said stock flow control means also further including circuit means connecting said flow sensing means and said speed sensing means to said stock flow control means and for combining said first and second control signals to control said valve means;

3. A paper making machine according to claim 1 5 total flow control means including second valve means wherein said rst signal conversion means further includes, connected to said stock delivery means between said means for manually adjusting the amount of stock dedilution means and said headbox to receive said rst livered to said headbox. control signal;

4. Ina paper making machine including: 10 position sensing means connected to said slice to gena continuously moving porous forming surface; erate a third control signal in response to the amount a headboX for receiving a slurry of paper stock, said of open area of said slice, said third control signal headbox positioned in close proximity with said being delivered to said total flow control means surface; wherein said first and third control signals are coina slice formed in said headbox adjacent said surface for bined to control the flow 0f diluted stock to said delivering stock to said surface; headbox.

means for supplying stock; 6. In a paper making machine including:

stock delivery means connected between said headbox a Continuously moving Porous forming Surface; and said supply means for delivering stock to said a headhoX for receiving a Slurry of Paper Stock; headbox; a slice on said headbox positioned for delivering stock the improvement therein comprising speed sensing to Said Surface;

means for sensing the rate of travel of said surface meanS for Supplying Stock; and generating a first centro] signal in response stock delivery means connected between said headbox thereto; and said supply means for delivering stock, the imfirst stock ow control means connected in fluid com- Provement therein comPriSing, meanS for SenSing the munication with said stock delivery means for con- Speed of travel 0f Said Surface and generating a firSt trolling the amount of stock delivered to said headcontrol Signal indicative thereof; box; means for sensing the open area of said slice and genadjusting means for changing the open area 0f said erating a second control signal indicative thereof;

slice; iirst stock flow control means including valve means for slice sensing means for generating a second control sigcontrolling the lloW of Stock to Said headhoX;

nel in response to the open area of Said slice; means for sensing the stock ow through said stock first signal conversion means in control of said stock delivery means and Producing a third control Signal; new control means and 4connected to said speed first signal conversion means receiving said iirst, second sensing means and Said Slice sensing means for reand third control signals and connected to the valve eeiving Said inst and Second conn-o1 Signals whereby of said first stock flow control means for controlling variations in the rate of travel of said surface will the iioW of Said Stock io Said headbox to maintain cause a corresponding change in said stock flow conl constant ratio of Stock spouting Velocity to form' trol means to change the amount of stock delivered mg Surface Spoed and to maintain a constant basis to said headbox; 40 weight per unit length of forming wire;

a Second Stock now control means connected between second stock flow control means including second valve the stock Supply means and the nest Steek new eon means connected between said first stock flow control means; trol means and said supply means for delivering stock second signal conversion means receiving said first conto Saiiheadbox? ano nel signal; second signal conversion means connected to the secmanual selecting means connected to said second signal Ond.v.alve o.f said second OYV control means mld conversion Ineens and supplying Said nrst Signal receiving said first control signal to control said thereto, and said second signal conversion means Second Valve connected to said second stock flow control means to 7- in a PaPer making machine including Control it, a continuously moving porous forming surface;

5 In a paper making machine including: a headbox for receiving a slurry of paper stock, said a continuously forming wire having an active run and headbox posltloned m close proximity with said a return run; Slirfai a headbox for receiving a slurry of paper stock, said a Shce fqrmd m Sald hefldbox adiacent Said Surface headbox positioned in close proximity with said for dehvermg Stock to said surface; forming Wire; means for supplying stock;

a slice formed in said headbox adjacent said active run stock delivery means connected btwen sald headbqx for delivering Steek to said active run; and said supply means for delivering stock to said means for supplying stock; hedboxi stock delivery means connected between said headbox the Improvement. therem compnsmg Spee@ Sensmg and said supply for delivering stock to said headbox; means for snsmg the rate of trai/.el of a1d Surface dilution means connected to said stock delivery means and generatmg a first control Signal m response for diluting the stock delivered to said headbox; thereto; the improvement therein comprising, speed sensing transducer mans Sensing the ope? area of Said Slice means for sensing the rate of travel of said forming and pmducmg a Second control Slgnaii wire and generating a rst control signal in response rst stock. ow.contro1 mems. lnclufimg ai valve con' thereto; nected 1n fluid communication with said stock destock flow control means including valve means conlivery means, for Controlling the amount of Stock de' nected to said stock delivery means between said hvefed to said headboxi v supply means and Said dilution means; first signal conversion means connected to the valve of 110W sensing means Connected to said Stock delivery said first stock flow control means and connected to means between said supply means and Said dilution said speed sensing means and said transducer means means to sense the amount of stock delivered to for receiving Said iirSt and Second control Signals Said headbox and to generate a second control sigwhereby variations in the rate of travel of said surnal; and face will cause a corresponding change in said iirst stock ow control means to change the amount of stock delivered to said headbox; second stock ow control means including a second valve connected between said supply means and said first stock control means; second signal conversion means connected to the second valve of said second stock flow control means and receiving said first control signal to control said second valve; and means for diluting said stock between said first and second stock ow control means. 8. A paper making machine according to claim 7 comprising pump means between said dilution means and second stock flow control means for mixing the stock.

References Cited UNITED STATES PATENTS 3,000,438 9/ 1961 Alexander 162-259 3,077,924 2/ 1963 Eastwood 162-259 3,271,241 9/1966 Mumme 162-258X 3,293,120 12/1966 Harman, Ir. etal. 162-253 S. LEON BASHORE, Primary Examiner A. DANDREA, JR., Assistant Examiner U.S. C1. X.R. 162-258, 259, 263 

